1. Field of the Invention
The present invention relates to a mobile communication system in which a portable terminal accesses information source server apparatus existing on a network through a wireless communication line. More particularly, the present invention relates to a mobile communication system for reducing a time required for a portable terminal to access information source server apparatus, a wireless communication gateway server apparatus, a position information calculation system, a method for reducing a connection time in the system, and a record medium for recording therein a connection time reduction program.
2. Description of the Related Art
Recently, a function has been proposed in which a portable terminal accesses information source server apparatus existing on a network (especially, the Internet) and obtains information from the network.
FIG. 1 shows an example of a configuration of a system in which this portable terminal accesses the information source server apparatus existing on the network.
As shown in FIG. 1, a dedicated server apparatus referred to as a wireless communication gateway server apparatus 24 is installed at an access point to a network, in order to access the network from a portable terminal 20.
This wireless communication gateway server apparatus 24 and the portable terminal 20 are connected to each other through a wireless communication line. In this wireless communication line, a communication is done, for example, by using a communication protocol referred to as WAP (Wireless Application Protocol) optimized for the characteristic of a wireless communication and a portable terminal. Also, a communication between the wireless communication gateway server apparatus 24 and the information source server apparatus 26 on the network is done in accordance with a standard protocol for the network [for example, in a case of the Internet, an Internet standard protocol {for example, HTTP (Hyper-Text Transfer Protocol) and TCP (Transmission Control Protocol)}].
The wireless communication gateway server apparatus 24 has an executing device for executing: a process for carrying out a protocol conversion between a communication protocol on a wireless communication line and a standard protocol on a network on which the information source server apparatus 26 exists; a data conversion process, for example, a process in which if information stored in the information source server apparatus 26 on the network is a document written under a HTML (Hypertext Markup Language) type, this document in the HTML type is converted into a document in a WML (Wireless Application Language) type used in the WAP; and a process in which if a document stored in information source server apparatus S on a network is, for example, a WML document in a text type, it is converted into a binary type, and then a data is compressed.
Also, the wireless communication gateway server apparatus 24 has a buffer memory emulator 25, as shown in FIG. 1. In this apparatus, in order to solve the unstableness in a communication condition caused by a band width and a delay amount in a wireless data communication network and an intermission in a wireless communication line, this buffer memory emulator 25 transiently stores therein a data sent by the information source server apparatus. The data for the buffer memory emulator 25 means, for example a memory size and a consumed size of the buffer memory 2. The consumed size means, for example a size used for storing the information from the information source server apparatus 7. Then, it monitors a condition of a buffer memory at a portable terminal, carries out a control so that the data does not overflow the buffer memory, and sends the data to the portable terminal.
Moreover, the portable terminal can be freely moved. Thus, it is necessary that a current area in which the portable terminal itself presently exists is always reported to a system side (a switching station) (this function is referred to as a position register).
The method for registering a position will be described below. An area number indicative of a position register area is always reported by a base station (not shown). The portable terminal 20 always compares an area number stored in the self-terminal with the reported area number, and sends a position register signal through the base station to a switching apparatus if those area numbers do not coincide with each other. The switching apparatus converts the position register signal sent by the portable terminal into a position information on which a line setting can be performed, and then registers it in a position information database 23. Thus, the system side can recognize a new position of the portable terminal 20. Hence, for example, if this portable terminal is accessed, a switching apparatus 22 can send a number information of the portable terminal to the position information database 23 and thereby connect a call to a desirable portable terminal, in accordance with information indicative of a position in which the portable terminal exists, from the number information fed back from the position information database 23.
The method for the portable terminal 20 to access the information source server apparatus 26 on the network will be described below, in the mobile communication system having the above-mentioned configuration. At first, when a power source of the portable terminal 20 is turned on, a position information of the portable terminal 20 is registered in the position information database 23 through the nearest base station. Next, since this portable terminal 20 issues a call to a telephone number of an access point which is registered in advance, a call is established between it and a wireless communication gateway server apparatus 24 having the access point.
An access request to the information source server apparatus 26 from the portable terminal 20 is reported to the wireless communication gateway server apparatus in a suitable wireless data protocol, for example, in the HTTP or WAP. So, it is possible to select and specify information source server apparatus by using URL (Uniform Resource Locator).
However, in the above-mentioned conventional mobile communication system, when the portable terminal accesses the information source server apparatus existing on the network, it must telephone a registered telephone number of only one access point assigned to the portable terminal, and then access the network through this access point. Thus, if a congestion is induced in this access point, a user of the portable terminal must again telephone the access point after a while. Also, it is impossible to obtain an insurance that the user can access the network after an elapse of a predetermined time.
If the demand from the users becomes equal to or greater than the number of terminals (the congestion state) that can be accommodated in the access point used when the wireless communication gateway server apparatus and the portable terminal communicate with each other, it is necessary to separately install the access point used by the portable terminal, in order to reduce a connection wait time of the user. At this time, a process for initializing a buffer memory within the wireless communication gateway server apparatus just before must be initialized. Hence, the user must wait by a time necessary for the initialization and a time for the connection to another access point.
If because of the movement of the portable terminal or the occurrence of the congestion in the access point disables the establishment of the connection to the wireless communication gateway server apparatus used just before, the connection to the wireless communication gateway server apparatus is done through another access point. However, even in this case, it is necessary to initialize the process for monitoring the buffer memory. In this case, the user must further wait by the switching time in the wireless communication gateway server apparatuses, in addition to the above-mentioned delay time. The fact that the user must wait not only results in a waste of a communication line resource, but also imposes an economic burden on the user when a communication fee or a service accounting based on a time is charged.
The techniques with regard to the switched capacitor type digital-analog converter are disclosed in Japanese Laid Open Patent Application (JP-A-H7-264662), Japanese Laid Open Patent Application (JP-A-H9-130861), Japanese Laid Open Patent Application (JP-A-H10-210533), Japanese Laid Open Patent Application (JP-A-H10-327454) and Japanese Laid Open Patent Application (JP-A-H11-83976).
The present invention is accomplished in view of the above mentioned problems.